CN-122014582-A - Digital control method for reciprocating piston compressor

CN122014582ACN 122014582 ACN122014582 ACN 122014582ACN-122014582-A

Abstract

The invention discloses a digital control method of a reciprocating piston compressor, which comprises the steps of 1) rechecking each stage of interstage pressure through a power saving principle or a manual given process, 2) calculating each stage (column) virtual cylinder working volume and cylinder state volume through each stage of operation conditions, 3) calculating and obtaining a complete set omega i of loading state data of a stepless back flow regulating device (theta axi ,θ cyi ), 4) carrying out dynamic safety rechecking and maximum optimization of reverse angles of each data pair (theta axi ,θ cyi ) in the complete set omega i , obtaining an instruction solution set phi i for regulating and controlling each stage (column) stepless back flow regulating device, and solving any data pair solution (theta axi ,θ cyi ) in the solution set phi i to generate a control instruction, wherein the method is a reciprocating piston compressor control method of a virtual cylinder concept, multivariable synchronous regulation, interstage pressure dynamic distribution and digital framework technology. The regulation and control efficiency of the large reciprocating compressor is improved, the equipment utilization rate of the large reciprocating compressor is improved, and the service life of the equipment is prolonged.

Inventors

WANG YAN
WU GUANGYU

Assignees

中石化广州工程有限公司
中石化炼化工程（集团）股份有限公司

Dates

Publication Date: 20260512
Application Date: 20241112

Claims (6)

1. A digital control method for reciprocating piston compressor, which is characterized in that a stepless reflux regulating device is arranged on the shaft side and the cover side of each stage (row) of air cylinder of the compressor, and the method is characterized in that: when the regulating variable changes, a control instruction for the stepless reflux regulating device is formed through the following steps of: 1) Rechecking each stage of inter-stage pressure through a power saving principle or a manual given process; 2) Accounting for each stage (bank) of virtual cylinder working volume and cylinder state volume by each stage of operating conditions; 3) Calculating and obtaining a complete set omega i of the loading state data pair (theta axi ,θ cyi ) of the stepless reflux regulating device; 4) And (3) carrying out dynamic safety rechecking and reverse angle maximization optimization of each data pair (theta axi ,θ cyi ) in the corpus omega i , obtaining an instruction solution set phi i for regulating and controlling each stage (column) stepless backflow regulating device, and solving any data pair solution (theta axi ,θ cyi ) in the solution set phi i to generate a control instruction.
2. The method for digitally controlling a reciprocating piston compressor of claim 1, wherein: in the step (1) of the above-mentioned process, The inter-stage pressure of each stage is rechecked through a power saving principle or a manual given process, and the operation mode of the compressor can be changed and is selected into three modes of equal-ratio compression modes of each stage, equal-load compression modes of each stage and manual distribution of the pressure ratio modes of each stage. When each level of equal ratio compression mode is selected, the pressure ratio values of each level are equal, and the relational expression is: Where ε i represents the i-th stage pressure ratio, P s represents the compressor inlet pressure, P d represents the compressor final discharge pressure, and P s(i+1) represents the (i+1) -th stage inlet pressure. When the equal load compression modes of all stages are selected, the shaft powers of the compression processes of all stages are equal or similar, the corresponding pressure ratios (P s(i+1) /P si ) of all stages are obtained after the shaft powers N i of all stages are equal by trial calculation through interpolation, and the calculation expression of the i-th shaft power N i is that Wherein N i represents the i-th level shaft power, eta mi represents the i-th level mechanical efficiency (the value range of a medium-sized or large-sized machine is 0.86-0.96, and the value range of a small-sized machine eta mi is 0.85-0.92); When the mode of manually distributing the pressure ratios is selected, the pressure ratios are obtained by manual input, and after the operation mode of the compressor is selected, the pressure ratios and the inter-stage pressure check values of the stages are generated. In the step 2) of the above-mentioned process, When each stage (row) virtual cylinder working volume V fi and cylinder state volume V dsi are calculated by each stage operating conditions, the calculation expression is: V dsi ＝V fi ·η vi V fi ＝V si ·ψ fti (i=1,...,N) wherein V dsi represents the state volume of the ith cylinder, V fi represents the ith virtual cylinder working volume, V si represents the ith real cylinder working volume, P si represents the ith intake pressure, Q 0 represents the volume flow in the standard state, T si represents the ith intake temperature, N represents the compressor speed, Q represents the number of peer cylinders of the ith stage, η vi represents the ith volumetric efficiency, ψ fti represents the ith total unloading coefficient, N represents the total number of stages of the compressor, i represents the number of stages variable of the compressor, and the value range is (i=1,..n); When the i-th stage cylinder is of a double-acting type and the piston rod does not penetrate, the total unloading coefficient psi fti is expressed as a volume allocation proportional relation represented by a shaft side unloading coefficient psi fai and a cover side unloading coefficient psi fci : S fai ＝S·ψ fai S fci ＝S·ψ fci Wherein D i represents the i-th stage real cylinder diameter, D represents the piston rod diameter, S represents the real piston stroke, S fai represents the i-th stage shaft side virtual stroke, S fci represents the i-th stage cap side virtual stroke; When the cylinder shaft side or the cover side stepless backflow regulating device loads the cylinder respectively, the relation expression between the crank angle theta and the ith stage shaft side or cover side virtual stroke S fai or S fci is as follows: Wherein r represents crank radius, lambda represents the ratio of crank radius (r) to connecting rod length (l) (lambda=r/l, abbreviated as connecting rod ratio), theta represents crank angle, namely the included angle between the crank and the cylinder center line, the crank angle is set by taking the outer dead point of the piston motion as the initial angle, the value range of theta is more than or equal to 0 DEG and less than or equal to 360 DEG, theta ai represents the corresponding crank angle when the ith stage cylinder shaft is loaded, and theta ci represents the corresponding crank angle when the ith stage cylinder head is loaded; In the step 3) of the above-mentioned process, When solving the complete set omega i of the loading state data pair (theta axi ,θ cyi ) of the stepless reflux regulating device, the method is as follows: For a certain standard volume flow Q z0 of the compressor, the ith stage may correspond to a plurality of groups of combinations of cylinder shaft side and cover side loading states (meeting the flow requirements), that is, corresponds to a plurality of groups of data pairs (θ axi ,θ cyi ), and records that the ensemble of the ith stage data pairs corresponding to the flow Q z0 is Ω i , where the relational expression is: Ω i (Q z0 )＝{(θ a1i ,θ c1i ),(θ a2i ,θ c2i ),…,(θ axi ,θ cyi )}(i＝1,…,N) Corresponding to a certain standard state volume flow Q z0 , a functional relation f 1 exists between the state volume V dsi of the ith cylinder and the loading state data pair corpus omega i (Q z0 ), and the expression is as follows: V dsi ＝f 1 (Ω i (Q Z0 ))(i=1,...,N) The total set omega i of the loading state data pair (theta axi ,θ cyi ) of the stepless reflux regulating device is obtained, so that the total regulation and control of the virtual cylinder volume and the cylinder state volume of each stage (row) are realized, and the reclassified interstage pressure of the compressor is ensured; In the step 4) of the above-mentioned process, When the dynamic safety check and the reverse angle maximization optimization of each data pair (theta axi ,θ cyi ) in the corpus omega i are carried out, the method is as follows: Wherein, F gi represents the i-th gas force, F gmax represents the maximum allowable gas force of the compressor, F pi represents the i-th comprehensive piston force, F pmax represents the maximum allowable comprehensive piston force of the compressor, theta αi represents the working reverse angle of the cross pin bearing of each revolution of the i-th cylinder, and F 2 represents the functional relationship; The data pair (theta axi ,θ cyi ) satisfying the function equation is marked as phi i (Q z0 ) and any data pair solution in phi i (Q z0 ) is called, so that a group of control instructions for the shaft side and the cover side of the stepless reflux regulating device can be generated.
3. The method for digitally controlling a reciprocating piston compressor of claim 2, wherein: The gas force, reciprocating inertia force and reciprocating friction force of each row of cylinders of the compressor are all along the direction of the center line of the cylinders, the algebraic sum of the gas force, the reciprocating inertia force and the reciprocating friction force is called as comprehensive piston force, and the calculation expression is that F pi ＝F gi +F si +F fi Wherein F si represents the i-th column reciprocating inertial force, and F fi represents the i-th column reciprocating frictional force; The gas force F gi and the reciprocating inertial force F si of the ith row have the following calculation expression when the cylinder of the ith row is double-acting and the piston rod does not penetrate F si ＝m si ·r·ω 2 (cosθ+λcos2θ) Wherein P ai represents the i-th row axial side cylinder pressure, P ci represents the i-th row head side cylinder pressure, P b represents the atmospheric pressure, the ranges of variation of P ai and P ci are the i-th row intake and exhaust pressures (P si ,P s(i+1) ), ω represents the rotational angular velocity (ω=n·pi/30), and m si is the total mass of the i-th row reciprocating motion; the i-th column reciprocating friction force F fi is opposite to the moving direction of the moving part, and makes the reciprocating friction force at the dead point be zero. When simplifying the calculation, F fi can be regarded as a certain constant value. Setting the minimum indexing angle of theta to be 1 DEG, taking the i-th row cylinder loading state data pair corpus omega i (Q z0 as a sample space, calculating the reciprocating friction force F fi , the reciprocating inertia force F si and the gas force F gi of each row in the full-peripheral angle working range under the loading condition of different data pairs (theta axi ,θ cyi ), and superposing and synthesizing the comprehensive piston force F pi of each row according to the phase angle so as to carry out dynamic safety rechecking and the maximization optimization of each row of reverse angle. The i-th column integrated piston force F pi is a function of crank angle θ, and when the value of F pi is zero, the stress direction of the cross pin bearing starts to be reversed. In one working period, if F pi only appears one zero value, the pin bearing working reverse angle is 180 degrees, if F pi appears two or more zero values, the corresponding crank angle theta 1 、θ 2 、…θ n (n is even number) needs to be calculated, and the pin bearing working reverse angle calculation formula is that θ α ＝min(sum((θ 2 -θ 1 )+…+(θ n -θ n-1 )),360°-sum((θ 2 -θ 1 )+…+(θ n -θ n-1 ))) Wherein, theta α represents the working reverse angle of each cross pin bearing, and theta 1 、θ 2 、…θ n (n is an even number) represents each crank angle corresponding to zero comprehensive piston force; The i-th row cylinder shaft side and cover side loading state data pair (theta axi ,θ cyi ) has a functional relation f 2 with the pin bearing working reverse angle (theta αi ) and has the expression that θ αi ＝f 2 (θ axi ,θ cyi ) For a certain nominal volume flow Q z0 of the compressor, the relation expression between the maximum working reverse angle max (theta αi ) of the pin bearing and the full set of loaded state data pairs omega i (Q z0 is that max(θ αi )＝max(f 2 (Ω i (Q Z0 )))(i=1,...,N) Meanwhile, the maximum working reverse angle of the pin bearing is larger than or equal to the minimum allowable value of the compressor, and a safety margin is reserved, and the expression is that max(θ αi )≥(15°~90°)(i=1,...,N)
4. The method for digitally controlling a reciprocating piston compressor of claim 1, wherein: The stepless backflow regulating devices are respectively arranged on the shaft side and the cover side of each stage (row) of air cylinder of the compressor, and the stepless backflow regulating devices can be in various realization modes and are typically characterized in that the closing time of an air suction valve is controllable, so that the air in the air cylinder can flow back to an air suction cavity before being compressed.
5. The method for digitally controlling a reciprocating piston compressor of claim 1, wherein: The data sources required by the calculation of the compressor are mainly divided into three parts, namely a regulating variable, a state parameter and mechanical modeling data, wherein the regulating variable of an external control system is a single variable or multiple variables, the variables are real-time transmission data or manual given, the state parameter is derived from the external control system, and the mechanical modeling data is derived from basic data input manually.
6. The method for digitally controlling a reciprocating piston compressor of claim 1, wherein: When the compressor completes the regulation and control action, firstly judging whether each stepless backflow regulating device is normal, if the running state is normal, completing the regulation and control function by the stepless backflow regulating device, and if the running state is abnormal, completing the regulation and control function by the return line regulating valves of each stage.

Description

Digital control method for reciprocating piston compressor Technical Field The invention belongs to the field of design and manufacture of compressors, and particularly relates to a digital control method of a reciprocating piston compressor. Background Reciprocating piston compressors are widely used in many fields and industries, and are generally designed and manufactured with a maximum flow rate and a maximum pressure ratio for the applied operating conditions, while reciprocating piston compressors have the characteristic of substantially constant volumetric flow rate under the designed operating conditions, which affect their operation and regulation under the variable operating conditions. At present, a large-sized reciprocating piston compressor is commonly used in single variable occasions (occasions requiring only one main variable in the control process and requiring other operation parameters to be kept stable), and the regulation and control means comprise setting a clearance cavity, a bypass return line, a full-stroke top-open suction valve or a partial-stroke top-open suction valve and the like. These adjusting means can be used singly or in combination, and they are characterized in terms of equipment investment, energy saving, consumption reduction and applicability. The closing time of the suction valve is accurately controlled by a special actuating mechanism when part of the stroke pushes up the suction valve, so that gas in the cylinder can flow back to the suction cavity through the suction valve before being compressed, the flow of the actual compressed gas is changed, stepless regulation in the control process can be realized through the device, and the stepless backflow regulating device is an important regulating means. When the large reciprocating piston compressor is applied to single variable occasions, the common regulation and control mode is relatively single, the basic control means is used for stabilizing the interstage pressure of each stage, and the regulation and control thought causes the compressor to have poor effect in some occasions. For example, when the inlet pressure of the compressor fluctuates greatly (the inlet pressure is the main variable), and the downstream demand (the outlet pressure and the gas flow rate) is stable, the conventional regulation mode is that the compressor still keeps the outlet pressure of each stage stable along with the great fluctuation of the inlet pressure, and the standard state flow rate of each stage is kept unchanged through the tracking regulation of the return line regulating valve. When the inlet pressure of the compressor is reduced or increased to the outlet pressure of a certain stage, the air inlet valve of the stage is forcibly unloaded, so that the empty load operation of the cylinder of the stage is realized, and the follow-up control of the inlet pressure which is a single variable is realized. The control mode can solve the problems that 1, the unloading of the air inlet valve is required to be matched with the return line regulating valve for operation, the control process is complex, the backflow power consumption cannot be avoided, and the long-period operation risk of the unloading cylinder is high. 2. The imbalance between the compressor and the dynamic column piston forces increases the load difference of the piston forces at each stage, the uniformity of the tangential force of the crankshaft is deteriorated, and the running stability of the compressor is challenged. 3. The pressure ratio of each stage of the compressor cannot be reasonably distributed, the interstage cooling is not fully utilized to reduce the compression work of the next stage and reduce the exhaust temperature, and the operation energy consumption of the compressor is increased. When the reciprocating piston compressor is applied to multiple (regulation) variable occasions (occasions requiring two or more main variables in the control process and other operation parameters to be kept stable), for example, in the previous example, the outlet pressure in the process of greatly fluctuating inlet pressure of the compressor also fluctuates (double regulation variable operation), and the control scheme is limited or even difficult due to the constraint of the original regulation mode. The result is that the stepless reflux regulation means and the reciprocating compressor control are not fused in depth digitalization, and the existing control process is not innovated, so that a digital control method of the reciprocating piston compressor is very necessary to be provided, and the operation requirement of multiple (regulation) variables of the piston machine is more reasonably and more efficiently met. Disclosure of Invention In order to solve the defects in the prior art, the application discloses a digital control method of a reciprocating piston compressor by using a technical scheme of virtual cylinder concept, multivariable synchronous regulat